Field of the Invention
The present invention relates to a dust collector device, and more particularly, to long bag filters that improve the non-uniformity of filtration velocity distribution along the length of the long bag filters by adjusting air permeability in the longitudinal direction of the bags, thereby improving filtration performance and reducing footprint and both of capital and operational costs of the dust collector using the long bag filters.
Description of the Related Art
Dust collectors using bag filters as a means of removing dust from gas stream occupy more than 80% in the market of small and medium size dust collectors. In accordance with the strengthening regulations for dust emission and working environments, a demand for industrial dust collectors has been gradually increased.
However, most industrial complexes in which many dust emitting companies gather have been in operation for more than 20 years since they were built, and the space for environmental facilities including filter dust collectors becomes saturated. Therefore, a plan for reducing the footprint of the filter dust collectors should be sought. For this, it is necessary to develop a dust collector that can be installed in a limited area and operated at low costs while maintaining high collection efficiency. As illustrated in FIG. 1, a typical dust collection system 1000 includes a dust source 200, a filter dust collector 100 and a blower 300.
A treatment gas containing dust generated from the dust source 200 moves to an inlet chamber 110 of the filter dust collector 100, is filtered through the bag filters 160, and moves to a discharge chamber 120. The blower 300 is connected to the discharge chamber 120 to form a negative pressure in the discharge chamber 120.
The bag filters 160 may be made of various materials in different shapes. However, a typical bag filter 160 is made of woven or nonwoven filter medium in a tubular shape, and has an opening part 161 and an inner space defined by the filter medium.
The bag filter 160 communicates with the discharge chamber 120 through the opening part 161 and a negative pressure is formed in the discharge chamber 120, such that the treatment gas in the inlet chamber 110 is introduced into the bag filter to be filtered while passing through the filter medium thereof, then moves to the discharge chamber 120 through the opening part 161 to be discharged.
A conventional filter dust collector mainly uses bag filters having a length of 3 m or less, but as described above, in order to reduce the footprint of the dust collector, long bag filters having a length of 10 m or more should be used. The footprint of a dust collector using 10 m long bag filters can be reduced by 50% or more as compared to a dust collector using bag filters having a length of 3 m, thereby reducing both of capital and operational costs.
However, a problem entailed in an application of long bag filters is that, as the bag filter length is increased, the filtration velocity of the treatment gas shows a severely biased distribution along the filter length.
A large unbalance occurs in a distribution of the filtration velocity along the bag filter length, which has a form that the filtration velocity is rapidly increased toward the opening part of bag filter and is rapidly decreased as it becomes further away from the opening part of bag filter. In this regard, as the length of bag filter is increased, such the phenomenon becomes more deteriorated (see FIGS. 2 and 3).
Herein, the filtration velocity refers to a velocity of the treatment gas introduced in a perpendicular direction to the filter medium. An average filtration velocity represents a flow rate of the treatment gas passing through unit surface area of bag filter, and a typical filter dust collector has an average filtration velocity in a range of 0.5 to 2.0 m/min.
A graph of FIG. 3 shows a filtration velocity distribution along the length of a bag filter having a diameter of 160 mm and a length of 3 m, 10 m and 15 m, respectively, at an average filtration velocity of 1.5 m/min. FIG. 3 is a graph illustrating the filtration velocity distribution, wherein a horizontal axis represents the bag filter length and a vertical axis represents the filtration velocity, respectively. That is, a value of 10 of the horizontal axis means that the bag filter opening part is located at a point of 10 m from a bottom of the bag filter. As illustrated in FIG. 3, in the case of the 10 m bag filter, about 70% of the treatment gas passes through the bag filter in the vicinity of the opening part which occupies about 30% of the entire filtration area.
This is equivalent to operating the bag filter having a length of about 3 m at an extremely higher filtration velocity than the typical filtration velocity, thus to be abnormally operated. In this case, the pressure drop across the 10 m long bag filter becomes much higher than that of 3 m long bag filter for the same average filtration velocity, and the filter medium of 10 m long bag becomes clogged only at a region of a high filtration velocity, resulting in shorter life-span of the bag filter and reduction of filtration performance. As a result, it is hard to expect to take advantages, which can be obtained by applying long bag filters, and the operation stability of the dust collector is deteriorated, such that the industrial process or the production process in which the treatment gas is generated may not be normally operated.
That is, since the treatment gas is filtered with being biased to a portion close to the opening part of the long bag filter, more amount of dust is deposited in the vicinity of the opening part in the entire length of the bag filter, and thereby reducing the life-span of the bag filter and increasing maintenance costs.
In general, in order to clean the dust loaded filters, pulse jet cleaning methods, which detach dust cake formed on the filter surface by instantaneously injecting a compressed air into the bag to physically inflate the bag filter, are largely used. If non-uniformity of filtration velocity in a longitudinal direction of the long bag filter is large, the dust is accumulated biasedly in the vicinity of the opening part of the bag filter, such that the filter cleaning frequency is decreased, which also causes a problem of shortening the life-span of the filter or increasing the operational costs.
As an example of the dust collector, there is a dust collecting apparatus using bag filters disclosed in Korean Patent Registration No. 10-1475866 (published on Dec. 23, 2014).